Glycogen Synthase Kinase 3 (GSK3) proteins are important regulators of a number of processes including WNT signaling. We have been studying a novel GSK3 in Drosophila, mjl, that is required for male fertility. The gene is active specifically in male germline cells and only after the onset of metamorphosis. The gene is a relative newcomer, as it is found in the genus Drosophila, but not in other sequenced genomes. It appears to have arisen by retrotranscription of an mRNA encoding a particular GSK3 isoform followed by insertion in a new location. We are currently focusing on the function of mjl.[unreadable] [unreadable] The doublesex gene encoded two members of the DMRT family of transcription factors, a male-specific (DSXM) and a female-specific (DSXF) isoform. We have determined that DSXM is expressed in all the somatic cells that are in contact with the male germline from gonad formation to terminal differentiation begins following meiosis. This pattern, along with the fact that DSX is non-cell-autonomously required for male germline survival or perhaps stem cell renewal, suggests that DSXM directly regulates genes required for soma/germline communication in the male niche. We are determining what genes are regulated by DSXM.